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Complementary medicine could hinder cancer treatment

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by Cancer Research UK | News

20 January 2004

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Cancer patients who use herbal remedies and health supplements during conventional treatment may risk dangerous side effects, according to a new report published today in the British Journal of Cancer1.

Garlic, cod liver oil and St John’s Wort are among the most commonly taken supplements that could interfere with some standard cancer treatments.

More than 300 patients at London’s Royal Marsden Hospital completed multiple-choice questionnaires which revealed that over 50 per cent of them took herbal remedies or food supplements or both.

Scientists found that fewer than half those taking complementary medicine had discussed this with the doctor overseeing their conventional treatment.

The report also found that around one third of those patients were unsure of the purpose of the remedy they were taking. And 11 per cent of patients reported taking supplements higher than the recommended doses.

Earlier research has shown that some complementary medicines have dangerous side effects and may react badly with conventional treatments. For instance garlic and cod liver oil are anticoagulants and may exaggerate the effect of blood thinning drugs taken by some cancer patients. Remedies such as St John’s Wort can interfere with the action of hormones, antibiotics and chemotherapy.

Researchers were also concerned about echinacea which has effects on the immune system and may compromise some types of cancer treatments for lymphoma and leukemia.

The study, led by Dr Ursula Werneke at Homerton Hospital’s psychiatric unit in London, highlights the importance for conventional healthcare professionals to discuss complementary medicine with their patients and for doctors to ensure they are properly briefed on how health remedies interact with standard treatment.

She says: “The real problem is that doctors may not have the expert knowledge needed to deal with so many potential risks when patients are mixing conventional treatment with alternative remedies. They need to avoid uncritical encouragement. Also there is not always time to discuss it in routine outpatient clinics.

“As well as this patients will not always accept their doctors’ opinions and may argue that conventional cancer treatment is equally toxic.”

Among the most common remedies, taken by the patients in the study, were echinacea, evening primrose oil, and gingko. The most popular supplements were combinations of vitamins, cod liver oil and selenium.

The study revealed that more than 12 per cent of patients had been given health warnings from pharmacists and these mostly concerned lymphoma patients who were taking echinacea which can interfere with antibody treatment. Further warnings were given to individual patients for cod liver/fish oil, gingko, garlic, kava kava and beta-carotene.

Professor Robert Souhami, Director of Clinical and External Affairs at Cancer Research UK- which owns the British Journal of Cancer – says: “There is a tendency to believe that complementary medicines are always harmless. This is not the case.

“This research is very valuable in that it indicates more work needs to be done to get a clearer picture about how complementary medicines react with conventional drugs so patients can receive the best possible advice concerning their treatment.”


  1. British Journal of Cancer90 (2) pp.408-413